The present invention relates generally to microswitch arrays and microswitch array elements for switching electrical signal lines. The invention is applicable to the switching of telecommunications signal lines and it will be convenient to hereinafter describe the invention in relation to that exemplary, non limiting application.
Switching arrays are used in telecommunication applications, when a large number of telecommunication signal lines are required to be switched. Generally, such switching arrays are provided by the permanent connection of copper pairs to xe2x80x9cpillarsxe2x80x9d or underground boxes, requiring a technician to travel to the site of the box to change a connection.
In order to remotely alter the copper pair connections at the box without the need for a technician to travel to the site, there have been proposed switching arrays consisting of individual electro mechanical relays wired to printed circuit boards. However, this type of array is complex, requires the addition of various control modules and occupies a considerable amount of space. Further, current must be continuously provided through the relay coil in order to maintain the state of the relay. Since in many applications switching arrays elements are only rarely required to be switched, this results in an undesired power consumption.
It would therefore be desirable to provide a switching array and switching array element which ameliorates or overcomes one or more of the problems of known switching arrays.
It would also be desirable to provide a bi-stable broad band electrically transparent switching array and switching array element adapted to meet the needs of modern telecommunications signal switching.
It would also be desirable to provide a switching array and switching array element tat facilitates the remotely controllable, low power bi-stable switching of telecommunication signal lines.
With this in mind, one aspect of the present invention provides a bi-stable microswitch including a pair of contacts and an armature movable between a first position and a second position to selectively break or make the pair of contacts, the armature being latched in the second position by a magnetic path including a permanent magnet and a magnetisable element having a first Curie temperature wherein the armature is resiliently biased towards the first position when latched, and is movable from the second position to the first position upon heating of the magnetisable element to above the first Curie temperature.
Conveniently, the armature may include a fist section having a first thermal expansion coefficient and a second section having a second thermal expansion coefficient causing movement of the armature from the first position to the second position upon heating of the armature. Such an armature is known as a thermal bimorph actuator. As an example of materials suitable for the fabrication of the armature, the first section may be at least partially formed of permalloy whilst the second section may be at least partially formed of invar.
The bi-stable microswitch may further include a fist heating device formed on or proximate the armature. A second heating device may also be formed on or proximate the magnetisable element. One or more of the first and second heating devices may include an electrical resistance element.
Alternatively, heat may be applied to at least one of the armature and the magnetisable element by means of electromagnetic radiation. For example, microwave or other radiation may be applied by non-contact means from a remote location.
The magnetisable element may be at least partially formed from a NiCu alloy, such as thermalloy, the composition of the alloy being adjusted to set the first Curie temperature.
Conveniently, the permalloy may at least partially constitute the pair of contacts. The pair of contacts may be formed in or on an electrically isolating substrate. The magnetisable element may be formed in the substrate, and separated from the pair of contacts by an electrically isolating layer formed in or on the substrate. The pair of contacts and the magnetisable layer may be formed by micro machining techniques, involving such steps as etching or electro forming. The armature may comprise a cantilever ovehanging the pair of contacts. The armature may also be formed by micromachining techniques, such as electro forming.
Another aspect of the present invention provides an array of bi-stable microswitches as described hereabove. Each of the microswitches may be at least partly formed in a common substrate by micro machining techniques.